The nanostructure of three-dimensional scaffolds enhances the current density of microbial bioelectrochemical systems

VICTORIA FLEXER; CHEN, J.; DONOSE, B.C.; SHERRELL, P.; WALLACE, G.G.; KELLER, J.

Wollongong

Simposio; 8th Annual International Electromaterials Science Symposium; 2013

Australian Research Council (ARC) Centre of Excellence for Electromaterials Science (ACES)

In microbial bioelectrochemical systems, whole cells are used as biocatalysts to catalyse oxidation and reduction reactions. Microbial fuel cells are the classical and more widely studied example of bioelectrochemical systems, performing the double task of wastewater treatment and electricity generation. More recently, the concept has been extended to the possibility of generating higher value products than electricity. In a typical microbial system, the anode is used to harvest electrons from wastewater, while oxidising organic pollutants, with the electrons being used as reducing power in the cathode to create novel and valuable products.The viability of prospective applications of microbial bioelectrochemical systems is highly dependent on performance improvement, i.e. in current increase. Current production is dependent on the microbial consortia, bioelectrochemical reactor design, and electrode materials. While the first two key characteristics have been widely researched for more than a decade, until very recently, most of the work on bioelectrochemical systems used only commercially available carbonaceous materials.Here we report on a new prospective microbial electrode material bearing a hierarchical porous structure. A new method was recently developed to directly grow carbon nanotube (CNT) networks on any type of substrate. This is achieved by modifying the generally employed route of chemical vapour deposition (CVD) synthesis. The so called CNT NanoWeb, comprises entangled multi-wall carbon nanotubes integrated onto an underlying conductive carbon layer.[1, 2] CNT NanoWeb was directly grown on reticulated vitreous carbon (RVC) scaffold. The results show that the new electrode material combines the advantages of both CNT nanoWeb and an open three-dimensional scaffold. The biofilm is formed on top of CNT texture structure.A very high current density of 6.8 mA cm-2 (10.6 mA cm-3) was recorded at room temperature with only mild stirring, i.e. in the absence of forced flow through the electrode. This high current was the product of the combined effect of the carefully chosen hierarchical porosity. The macroporous structure hosts a large microbial loading, and at the same time allows good mass transport that supplies the high substrate needs and removes the undesirable products, mostly H+ in the current situation.The improved bioanode performance suggests that carbon nanotube nanostructure not only improves the bacterial attachment to the electrode surface but also enhances the extracellular electron transfer, and therefore boosts the current production.